When injection-molding parts, injection molding apparatus fitted back-to-back needle valve nozzles is used to feed a flowable material at a predetermined temperature and at high pressure to a plurality of separable mold inserts. The material to be processed is fed by a central fluid intake to a typically centrally configured main manifold plate. From there the material to be processed moves—optionally using one or several auxiliary manifold plates—into the valve needle nozzles injecting said material into the mold inserts. A system of flow ducts issuing into the needle valve nozzles is contained within the manifold plates. Said valve nozzles are fitted with valve needles that are driven pneumatically, hydraulically or electrically and periodically opening the gate apertures in the mold insert. This design enables accurate material metering and clean cutoff sites, in particular at high-speed operation. Where called for, the flowable material also may be injected in segmented manner, for instance in gate cascading.
Such a back-to-back injection molding apparatus is disclosed for instant the European patent document EP 1 184 152 A1. It comprises a main manifold plate which is fitted with several flow ducts and which receives the fluid to be processed from a central fluid intake. Then the fluid is moved through the main manifold plate's flow ducts to a plurality of needle valve nozzles received in nozzle receiving plates configured on each side of the main manifold plate. The needle valve nozzles of one of the nozzle receiving plate and those of the other nozzle receiving plate are configured oppositely each other in a back-to-back geometry. Sets of needle valve nozzles are combined into needle valve nozzle regions, each region being synchronously driven by a drive system. Each drive system comprises at least one adjustment drive mounted in one of the valve plates and a connecting element, the latter being driven by said adjustment drive and being connected with all valve needles of said nozzles of the corresponding region in order to thereby synchronously transmit the motion of the adjustment drive to all valve needles of one region.
The EP 1 184 152 A1 document incurs the substantive drawback that the drive systems' adjustment drives are configured in the nozzle plates that are exposed to substantial heating during injection molding, potentially entailing operational malfunctions. In particular when hydraulic or pneumatic adjustment drives are used, said high heats/temperatures may entail problems in sealing and in plunger guidance. Reliable injection molding is not assured. Moreover the individual valve needles cannot be driven individually, as is required/desirable in many applications.
The European patent document EP 0 893 226 A1 describes injection molding apparatus also comprising a central manifold plate fitted with several flow ducts. The flow ducts are fluidly connected to needle valve nozzles configured opposite each other in a back-to-back array. Each of said nozzles is fitted with a valve needle to open/close a nozzle aperture, all valve needles being driven independently for one another by pneumatically operating plunger units. The plungers units are configured in the manifold plate. While this feature allows significant injection molding apparatus compactness, on the other hand this design also incurs the drawbacks of the hot manifold plate during injection molding leading to sealing losses and to guidance problems in the plunger units.
In the light of the above stated art, one goal of the present invention is to offer an improved injection molding apparatus fitted with back-to-back valve needle nozzles, in particular offering compactness and manufacturing economy, extensively averting sealing problems and plunger-unit related difficulties affecting plunger guidance.